超宽带大功率合成器设计北大核心CSCD

在80 MHz~1 GHz频段,单个功率管输出功率能达到100 W以上,为研制输出功率400 W的功率放大器,文中设计了四路功率合成器。该合成器需要实现功率容量大、工作频带宽、体积小的设计目标。在功率容量方面,文中采用悬置带状线结构,其功率容量远远大于微带线结构;在工作频带方面,采用切比雪夫九节阻抗变换器,将工作带宽拓宽为80 MHz~1 GHz;在体积方面,文中合成器的功率合成部分采用Y型节级联实现四路功率合成,阻抗变换部分采用切比雪夫阻抗变换器进行阻抗变换,该结构相较于磁环巴伦功率合成器,不但具有损耗小、平坦度高的优点,而且通过将阻抗变换器设计成曲折的形状,进一步缩小了合成器体积。仿真与实测结果显示该合成器在80 MHz~1 GHz范围内还具有较高的平坦度,合成效率可达90%以上。     

Characterization and exposure assessment of household fine particulate matter pollution in China

Household fine particulate matter (PM_2.5) pollution greatly impacts residents' health. To explore the current national situation of household PM_2.5 pollution in China, a study was conducted based on literature published from 1998 to 2018. After extracting data from the literature in conformity with the requirements, the nationwide household-weighted mean concentration of household PM_2.5 (HPL) was calculated. Subgroup analyses of spatial, geographic, and temporal differences were also done. The estimated overall HPL in China was 132.2 ± 117.7 μg/m³. HPL in the rural area (164.3 ± 104.5 μg/m³) was higher than that in the urban area (123.9 ± 122.3 μg/m³). For HPLs of indoor sampling sites, the kitchen was the highest, followed by the bedroom and living room. There were significant differences of geographic distributions. The HPLs in the South were higher than the North in four seasons. The inhaled dose of household PM_2.5 among school-age children differed from provinces with the highest dose up to 5.9 μg/(kg·d). Countermeasures should be carried out to reduce indoor pollution and safeguard health urgently.     

基于熵权物元模型的长三角幸福河层次评价

将幸福河概念与长江三角洲区域一体化发展战略相结合，基于自然、人类社会、人水关系3个系统构建了包含24个指标的长三角幸福河层次评价指标体系；引入需求层次理论，以基础Ⅰ层次、基础Ⅱ层次、提升Ⅰ层次、提升Ⅱ层次、幸福层次5个层次作为幸福河的层次评价等级，运用熵权物元模型，建立了长三角幸福河层次评价模型，并对2018年长三角三省一市幸福河层次等级进行了评价。结果表明，三省一市均处于转化中的中间状态，其中江苏省向提升Ⅰ层次转化，浙江省、安徽省向提升Ⅱ层次转化，上海市向幸福层次转化，说明区域整体幸福河层次处于较高水平，但稳定性较差。     

Real-time molecular characterization of air pollutants in a Hong Kong residence: Implication of indoor source emissions and heterogeneous chemistry

Due to the high health risks associated with indoor air pollutants and long-term exposure, indoor air quality has received increasing attention. In this study, we put emphasis on the molecular composition, source emissions, and chemical aging of air pollutants in a residence with designed activities mimicking ordinary Hong Kong homes. More than 150 air pollutants were detected at molecular level, 87 of which were quantified at a time resolution of not less than 1 hour. The indoor-to-outdoor ratios were higher than 1 for most of the primary air pollutants, due to emissions of indoor activities and indoor backgrounds (especially for aldehydes). In contrast, many secondary air pollutants exhibited higher concentrations in outdoor air. Painting ranked first in aldehyde emissions, which also caused great enhancement of aromatics. Incense burning had the highest emissions of particle-phase organics, with vanillic acid and syringic acid as markers. The other noteworthy fingerprints enabled by online measurements included linoleic acid, cholesterol, and oleic acid for cooking, 2,5-dimethylfuran, stigmasterol, iso-/anteiso-alkanes, and fructose isomers for smoking, C₂₈-C₃₄ even n-alkanes for candle burning, and monoterpenes for the use of air freshener, cleaning agents, and camphor oil. We showed clear evidence of chemical aging of cooking emissions, giving a hint of indoor heterogeneous chemistry. This study highlights the value of organic molecules measured at high time resolutions in enhancing our knowledge on indoor air quality.     

典型废玻璃回收厂区空气颗粒物及噪声分布特征研究

以某典型废玻璃回收厂区作为研究对象, 监测和分析了车间及厂区内部的噪声强度、空气颗粒物(PM_2.5、PM₁₀) 浓度等环境指标, 点位布设涵盖了车间入口、人工分拣、物料筛分、破碎、干法清洗等关键工艺环节; 其次, 解析了空气颗粒物的组分及形貌特征, 并对其在厂区及车间内部的时空分布特征进行了研究; 此外, 利用噪声控制模型模拟并分析了隔声罩对噪声的控制作用。结果表明, 生产车间中工作态的空气颗粒物浓度显著高于非工作态, 其中干法清洗区浓度最高, 其PM_2.5 浓度为3.725 mg/m³, PM₁₀浓度为4.055 mg/m³; 噪声监测结果显示生产车间内噪声强度较高, 达到99.5 dB, 而引入隔声罩后噪声强度可降至67 dB, 结果表明, 隔声罩可有效控制频率为125~1 000 Hz 的噪声。该研究可为废玻璃的绿色、高效回收处置提供理论基础和实践经验。     

Effect of hydrogen supplementation on engine performance and emissions

Vehicular Pollution and environmental degradation are on the rise with increasing vehicles and to stop this strict regulation have been put on vehicular emissions. Also, the depleting fossil fuels are of great concern for energy security. This has motivated the researchers to invest considerable resources in finding cleaner burning, sustainable and renewable fuels. However renewable fuels independently are not sufficient to deal with the problem at hand due to supply constraints. Hence, advanced combustion technologies such as homogeneous charge compression ignition (HCCI), low-temperature combustion (LTC), and dual fuel engines are extensively researched upon. In this context, this work investigates dual fuel mode combustion using a constant speed diesel engine, operated using hydrogen and diesel. The engine is operated at 25, 50 and 75% loads and substitution of diesel energy with hydrogen energy is done as 0, 5, 10 and 20%. The effect of hydrogen energy share (HES) enhancement on engine performance and emissions is investigated. In the tested range, slightly detrimental effect of HES on brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) is observed. Comparision of NO and NO₂ emissions is done to understand the non-thermal influence of H₂ on the NO_x emissions. Hence, HES is found beneficial in reducing harmful emissions at low and mid loads.     

基于广义隐马尔可夫模型的PM2.5浓度预测

近年来，以PM_2.5为主要污染物的重霾污染事件频频发生，给我国国民经济和居民健康造成了严重损失。在空气质量尚未得到根本性改善的情况下，对重霾污染的准确预警不仅能使公众合理回避污染危害，还能为政府实施应急管理提供时间裕量。针对影响PM_2.5浓度的前体物及气象因素的非高斯分布特点以及传统隐马尔可夫模型（hidden Markov model，HMM）必须已知隐含状态个数的缺点，采用广义隐马尔可夫模型（generalized hidden Markov model，GHMM）对北京市除去定陵外的11个国控站点2013年1月～2017年1月的PM_2.5浓度进行了预测。结果表明：GHMM对严重污染及以上PM_2.5样本浓度预测准确率显著高于传统连续HMM，但针对中度污染及以下PM_2.5样本浓度的预测准确率接近传统HMM。     

Supercharged Proteins and Polypeptides

Electrostatic interactions play a vital role in nature. Biomacromolecules such as proteins are orchestrated by electrostatics, among other intermolecular forces, to assemble and organize biochemistry. Natural proteins with a high net charge exist in a folded state or are unstructured and can be an inspiration for scientists to artificially supercharge other protein entities. Recent findings show that supercharging proteins allows for control of their properties such as temperature resistance and catalytic activity. One elegant method to transfer the favorable properties of supercharged proteins to other proteins is the fabrication of fusions. Genetically engineered, supercharged unstructured polypeptides (SUPs) are just one promising fusion tool. SUPs can also be complexed with artificial entities to yield thermotropic and lyotropic liquid crystals and liquids. These architectures represent novel bulk materials that are sensitive to external stimuli. Interestingly, SUPs undergo fluid–fluid phase separation to form coacervates. These coacervates can even be directly generated in living cells or can be combined with dissipative fiber assemblies that induce life-like features. Supercharged proteins and SUPs are developed into exciting classes of materials. Their synthesis, structures, and properties are summarized. Moreover, potential applications are highlighted and challenges are discussed.